Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $235.79   4.201%   $245.6955   $245.70   $245.70   $245.70  
  Purchase #2 $62.97   11.416%   $70.1587   $70.16   $70.15   $70.20  
  Purchase #3 $239.27   13.142%   $270.7149   $270.71   $270.70   $270.70  
  Purchase #4 $74.96   13.839%   $85.3337   $85.33   $85.35   $85.30  
  Purchase #5 $165.60   4.868%   $173.6614   $173.66   $173.65   $173.70  
  Purchase #6 $40.83   8.392%   $44.2565   $44.26   $44.25   $44.30  
  Purchase #7 $117.88   7.209%   $126.378   $126.38   $126.40   $126.40  
  7 purchase totals = $937.30       $1,016.1987   $1,016.20   $1,016.20   $1,016.30